BTE attempts to read specs while they're being written

[tokebe]

Rarely, it appears that BTE receives a query causing it to read the smartapi specs at the same time the cron job to update them is writing to the file, causing a SyntaxError with the message "unexpected end of JSON input".

This can be solved by caching the specs in redis and reading from that instead, while the cron job first writes the file, and then writes to redis. Redis handles ensuring read/write won't happen simultaneously.

[tokebe]

Note that this issue is rare enough, and its fix involved enough, that we're not targeting it for the (very much impending) Milestone.